A New 1D/2D Coupled Modeling Approach for a Riverine-Estuarine System Under Storm Events: Application to Delaware River Basin

Numerical simulations of three of the most severe historical tropical cyclones to affect the Delaware River Basin (DRB) are used to evaluate a new numerical approach that is a candidate model for the inland-coastal compound flood forecast. This study includes simulating interactions of tides/surges, freshwater streamflows, winds, and atmospheric pressure for the DRB. One-way coupling between the hydrologic (National Water Model [NWM]) and the ocean/wave (ADvanced CIRCulation model/WAVEWATCH III [ADCIRC/WW3]) models for the Delaware river-estuarine system is developed. The links between the coastal processes and the NWM are provided by two different hydraulic and hydrodynamic models: (i) a well-calibrated public-domain 1D hydraulic solver model (Hydrologic Engineering Center's River Analysis System [HEC-RAS]) and (ii) 1D/2D open-sourced hydrodynamic model (D-Flow Flexible Mesh [D-Flow FM]). First, the modeling system is tested to confirm model verification and stability when the system is forced with only tidal forcing. Then, the relative performance of each modeling approach (NWM/D-Flow FM/ADCIRC/WW3 and NWM/HEC-RAS/ADCIRC/WW3) is evaluated using observational data from Hurricanes Isabel (2003), Irene (2011), and Sandy (2012). Furthermore, the sensitivity of water level prediction to the streamflows, different wind products, and bed roughness are examined. Results show that the D-Flow FM is generally accurate for water levels: the water levels near the peak of the storms have askillranging from 0.79 to 0.91 with a negligible phase error. Simulations show that water level predictions depend on an accurate representation of the wind conditions and bottom roughness. The work shows that hydrodynamic predictions, especially upstream, are highly dependent on the streamflow discharges. Plain Language Summary The East Coast of the United States is prone to powerful winter nor'easters and tropical cyclones. Both weather patterns produce strong winds, large storm tides, enormous ocean waves, and potentially extreme precipitation. This makes the U.S. East Coast vulnerable to catastrophic damage and loss of life. The Delaware River Basin is part of the highly developed and densely populated megalopolis of the northeastern United States. The unique properties and movement of individual storms and the complexity of the coastal morphology require the implementation of the most skillful and comprehensive modeling approach for forecasting and planning purposes. In this paper, the appropriate modeling system is evaluated for the hurricanes that made landfall along the East Coast of the United States to investigate the compound inland-coastal flooding. Numerical results are compared with observational data from National Oceanographic and Atmospheric Administration (NOAA). In agreement with observations, simulations indicate that water level estimations depend on a precise representation of both river inflows and elevated sea levels. The findings of this work show that using the proposed modeling framework has advantages over existing river hydraulic models, particularly near a coastal plain estuary during storm events.